1. Field of the lnvention
The present invention relates generally to launch vehicle ordnance ignition system and in particular, to laser initiated ordnance (LIO) systems used for flight initiation and termination of launch vehicles.
2. State of the Art
Presently, launch Vehicles are used to propel devices (e.g., satellites) into space. For this purpose, energy sources such as solid and liquid fuel ordnances are provided. Electronic ordnance systems (OIS) are typically used to actuate the firing of an ordnance.
Upon initiation of a vehicle launch, there is a possibility of malfunction or error in launch trajectory and/or flight control. To account for such a situation, destruct charges are typically provided onboard the vehicle. These charges constitute a flight termination system (FTS), for destroying the vehicle while in motion. Flight termination destruct action involves simultaneously initiating destruct charges and other ordnance devices located throughout a launch vehicle.
Because of the potential risks involved in controlling the launch and flight trajectory of launch vehicles, range safety requirements are a key concern. These requirements primarily relate to OIS and FTS reliability standards. Currently, ordnance initiation systems do not comply with proposed range safety requirements.
For example, known electrical subsystems (e.g., exploding bridgewire firing units) for initiating ordnance activation in OIS or FTS control systems do not permit reliable testing. Further, the present explosive transfer assemblies (ETA) used to distribute energy to the various destruct charges limit OIS and FTS reliability to approximately 0.994, weigh a great deal, and are expensive and difficult to install. The electroexplosive devices (EED) used to initiate the present ETAs are also sensitive to stray voltages, and require the use of an in-line/out-of-line mechanical safe-arm device to protect against inadvertent EED detonation.
Presently known systems such as the Atlas, Delta, and Titan ordnance systems all have non-compliant ordnance control systems in need of replacement. Further, testing energy-measuring loads prior to hookup must be performed for the EED-based systems about 5 days prior to launch with the known test equipment during a flight program verification (flight simulator) exercise.
A general diagram of an exemplary, known Delta II 7925 FTS system is shown in FIG. 1. The system includes a first stage 703 with solid rocket motor (SRM) boosters, a second stage 704 and a third stage 705, and performs both thrust termination and destruct functions.
Thrust termination events, plotted on the left side of the figure, are electrically controlled valving operations set in motion by Arm Signals issued by the command destruct receivers 700, 701 (CDR) in response to a properly coded transmission from ground-based range safety transmitters. The first and second stage thrust termination functions do not involve ordnance and are not within the scope of the present invention. Third stage thrust prevention/termination is presently accomplished by having a third stage destruct explosive transfer assembly (ETA) sever an electrical harness.
For purposes of background information, the first stage SRM booster destruction is effected by arming and monitoring an electromechanical in-line/out-of-line safe & arm (S/A) 706 containing a pair of electro-explosive devices (EEDs) 707, 708 via the first stage umbilical 709. Upon transmission of a suitably coded destruct command from range safety (which generally follows the thrust-terminating arm command by several seconds), CDRs fire the EEDs with destruct signals by closing internal relays to +28 Vdc. In the case of the first stage S/A, one EED is fired by the CDR 710 in the first stage while the second is fired by CDR 701 in the second stage.
The EEDs detonate ETAs which transfer energy to two linear cutting charges 711, 712 that destruct the first stage LOX and fuel tanks 164, 166 and, via nine redundant quick-disconnect ETAs, to nine circular linear shaped charges (CLSCs) 713 one on the front dome of each SRM. Explosive harnesses 714, 715 interconnect both EEDs to all of these 11 destruct charges so that failure of one EED does not impede any destruct action.
As shown in FIG. 1, the Delta II 7925 configuration uses redundant linear destructor assemblies 711, 712 which longitudinally rupture the LOX tank 164 of the first stage destruct device along its full length and the fuel tank 166 along part of its length. The rupturing disperses the LOX and fuel into the atmosphere. Each 63.8-foot long linear destruct assembly consists of six strands of PETN 100 plastic primacord, two of which are coupled to an explosive harness via explosive relays and unions which in turn are coupled to the energy transfer system (ETS) which terminates at the S-A outputs.
In addition, explosive relays are used on the two coupled strands to improve the reliability of initiating the other four. The first stage ETS of the current Delta II is designed to transfer the high energy (detonation shock) from the FTS firing units (S/A) redundantly to each destruct device.
For the second and third stage destruction, an S/A identical to that in the first stage is located in the second stage and is armed and monitored via the second stage umbilical 716. Upon range safety destruct command, each of the two second stage CDRs fires one of the two EEDs. ETAs transfer detonation from the S/A to a linear shaped charge 170, which destructs the second stage propellant tanks, and to four conical shaped charges 183 (mounted on the second stage) which destruct the third stage SRM 180. Each of the two ETAs 176, 178 leading to the third stage destruct harness is dressed around the third stage event sequencing ignition wiring harness to cut this harness. There is no ordnance cross-over between the redundant second stage ETAs other than that provided by the 1D47087 linear shaped charge itself.
The Delta II 7925 configuration uses a single 3.5-foot length copper sheathed, 300 gr/ft (RDX) linear shaped charge (LSC) 170 configured in a U-shaped configuration as the second state destruct device. Both ends are terminated (butt joint only, no fitting) with redundant 27.3-foot long lengths of 100 gr/ft (PETN) detonating fuze. The butt joint is maintained by a heavy wall molded polyethylene part which also fits over the U-shaped length of LSC to maintain the required standoff. The redundant detonating fuze assembly is connected to redundant 6.1-foot lengths of 2.5 gr/ft (HNS) mild detonating cold (MDC) wrapped with multilayer fiberglass with an explosive relay and union. The opposite ends of the redundant MDCS attach to the S/A 172 located in a forward skirt of the second stage.
The U-shaped LSC mounts directly to both the fuel and oxidizer tanks 174 on the second stage. Upon destruct command, the two CDRs 700, 701, co-located with S/A 172 in the second stage, fire the S/A detonators which then initiate the LSC destruct device 170 to cut the tanks open causing the fuel and oxidizer to mix.
For third stage FTS, the Delta II 7925 configuration uses an ETS consisting of two strands of 70 gr/ft (PETN) primacord, each of which are connected on one end to the second stage ETS 716, 717 via ETAs 176 and 178 in FIG. 1. This connection is made using crimped explosive relays and a plastic tee. The opposite end of each primacord is routed through a hole in the aft end of two modified hemispherical-shaped charge destructors (MHSCD) which are mounted on the second stage side of a spintable structure. The charge destructors are represented as the conical charges 183 in FIG. 1.
The hole in each charge destructor is perpendicular to the centerline of the MHSCD and passes over a 68 milligram RDX booster pellet which is initiated by the side-breakout of the primacord detonation. The booster in turn initiates a 38 gram RDX main charge which then collapses the modified hemispherical linearly to create a high velocity jet.
The jet from each of the four MHSCDs 183 travels through air across the second stage/third stage interface (approximately 14.0 inches total) 185 to impact and rupture the solid rocket motor (SRM) case 180. The 38 gram MHSCs, commonly known as "oil-patch completion charges" in the industry, will produce a hole of 0.5 inch diameter in the motor case and the molten metal jet will cause the propellant to burn and vent outward through each hole produced. If either leg of the ETS fails, only two such holes are produced.
In addition, each leg of the ETS is routed around the third stage event sequencing system ignition wiring cable 182 enroute to MHSCDs. The side breakout of the primacord detonation cuts this cable to inhibit spin-up, separation, and solid motor ignition.
Presently, known energy transfer systems (ETS), such as the Delta II ETS are complex networks of various lengths of primacord, TLX, and FCDC (flexible confined detonating cord) all interconnected with a variety of explosive fittings, couplers, and relays. Further, in addition to deficient characteristics such as non-hermeticity and sensitivity, known destruct systems, such as that of FIG. 1, lacks inadvertent separation destruct system (ISDS) capabilities used with powered stages not containing CDRs.
Accordingly, there is a need for improved ordnance ignition systems having enhanced safety and reliability. Further, it is in the best safety management interest of the range safety agencies that any forthcoming OIS and FTS systems have as much in common as possible.